I've often found myself needing -- and thinking a/b building -- a webapp/site for taking/collecting screenshots of other sites. But I'm not sure it'd actually be useful and I certainly don't know if anyone'd pay for it.
http://cutycapt.sourceforge.net/ is one of better screen capture engines I found for OSX. Most are based on Webkit/QT and Xvfb for Unix support.
What I'm talking about is most like a screenshot version of archive.org.